Sphecius speciosus, often simply referred to as the cicada killer, is a large digger wasp species. Cicada killers are large, solitary wasps in the family Crabronidae. The name may be applied to any species of crabronid which uses cicadas as prey, though in North America it is typically applied to a single species, S. speciosus. However, since there are multiple species of related wasps, it is more appropriate to call it the eastern cicada killer. This species occurs in the eastern and midwest U.S. and southwards into Mexico and Central America. They are so named because they hunt cicadas and provision their nests with them. In North America they are sometimes called sand hornets, although they are not hornets, which belong to the family Vespidae.

The most recent review of this species' biology is found in the posthumously published comprehensive study by noted entomologist Howard Ensign Evans.^[1]

Description

Five female eastern cicada killers, Sphecius speciosus

Adult eastern cicada killer wasps are large, 1.5 to 5.0 centimetres (0.6 to 2.0 in) long, robust wasps with hairy, reddish and black areas on the thorax (middle part), and are black to reddish brown marked with light yellow stripes on the abdominal (rear) segments. The wings are brownish. Coloration superficially resembles that of some yellowjacket and hornet species. The females are somewhat larger than the males, and both are among the largest wasps seen in the Eastern United States, their unusual size giving them a uniquely fearsome appearance. European hornets (Vespa crabro) are often mistaken for Eastern cicada killers.

Life cycle and habits

A female Sphecius speciosus digging a burrow next to a driveway

This female cicada killer landed in the grass after becoming tired while carrying a cicada in flight and landed short of her burrow.

Eastern cicada killer wasp holding a paralyzed cicada at John Heinz National Wildlife Refuge

Solitary wasps (such as the eastern cicada killer) are very different in their behavior from the social wasps such as hornets, yellowjackets, and paper wasps. Cicada killer females use their sting to paralyze their prey (cicadas) rather than to defend their nests; unlike most social wasps and bees, they do not attempt to sting unless handled roughly. Adults feed on flower nectar and other plant sap exudates.

Adults emerge in summer, typically beginning around late June or early July and die off in September or October. They are present in a given area for 60 to 75 days, usually until mid-September. The large females are commonly seen skimming around lawns seeking good sites to dig burrows and searching for cicadas in trees and taller shrubs.

The males are more often seen in groups, vigorously challenging one another for position on the breeding aggregation from which they emerged, and generally investigate anything that moves or flies near them. It is not unusual to see two or three male wasps locked together in apparent midair combat, the aggregate adopting an erratic flight path until one of the wasps breaks away. The male wasp's aggressive behavior is similar to that of another robust insect of the area, the male carpenter bee. In both cases, while the males' vigorous territorial defense can be frightening and intimidating to human passersby, the males pose no danger whatsoever. They will only grapple with other insects, and cannot sting.

Cicada killer infestation: the reddish brown patches are cicada killer burrows.

This ground-burrowing wasp may be found in well-drained, sandy soils to loose clay in bare or grass-covered banks, berms and hills as well as next to raised sidewalks, driveways and patio slabs. Females may share a burrow, digging their own nest cells off the main tunnel. A typical burrow is 25–50 centimetres (10–20 in) deep and about 1.5 cm (0.59 in) wide. In digging a burrow, the female dislodges the soil with her jaws and, using her hind legs, pushes loose soil behind her as she backs out of the burrow. Her hind legs are equipped with special spines that help her push the dirt behind her. The excess soil pushed out of the burrow forms a mound with a trench through it at the burrow entrance. Cicada killers may nest in planters, window boxes, flower beds or under shrubs, ground cover, etc. Nests often are made in the full sun where vegetation is sparse.

After digging a nest chamber in the burrow, female cicada killers capture cicadas, paralyzing them with a sting. After paralyzing a cicada, the female wasp holds it upside down beneath her and takes off toward her burrow; this return flight to the burrow is difficult for the wasp because the cicada is often more than twice her weight. After putting one or more cicadas in her nest cell, the female deposits an egg on a cicada and closes the cell with dirt. Male eggs are laid on a single cicada but female eggs are given two or sometimes three cicadas; this is because the female wasp is twice as large as the male and must have more food. New nest cells are dug as necessary off of the main burrow tunnel and a single burrow may eventually have 10 or more nest cells. The egg hatches in one or two days, and the cicadas serve as food for the grub. The larvae complete their development in about 2 weeks. Overwintering occurs as a mature larva within an earth-coated cocoon. Pupation occurs in the nest cell in the spring and lasts 25 to 30 days. There is only one generation per year and no adults overwinter.

This wasp is frequently attacked by the parasitic "velvet ant" wasp, Dasymutilla occidentalis, also known as the "cow-killer" wasp. It lays an egg in the nest cell of the cicada killer, and when the cicada killer larva pupates, the parasitoid larva consumes the pupa.

Interaction with humans

A male eastern cicada killer guarding its territory and looking for females with which to mate

Although cicada killers are large, female cicada killer wasps are not aggressive and rarely sting unless they are grasped roughly, stepped upon with bare feet, or caught in clothing, etc. One author who has been stung indicates that, for him, the stings are not much more than a "pinprick".^[2] Males aggressively defend their perching areas on nesting sites against rival males but they have no sting. Although they appear to attack anything that moves near their territories, male cicada killers are actually investigating anything that might be a female cicada killer ready to mate. Such close inspection appears to many people to be an attack, but male and female cicada killers don't land on people and attempt to sting. If handled roughly females will sting, and males will jab with a sharp spine on the tip of their abdomen. Both sexes are well equipped to bite, as they have large jaws; however, they don't appear to grasp human skin and bite. They are non-aggressive towards humans and usually fly away when swatted at, instead of attacking. Cicada killers exert a measure of natural control on cicada populations and thus may directly benefit the deciduous trees upon which their cicada prey feed.

Other cicada killer wasps

The North American cicada killer wasps all belong to the genus Sphecius, of which there are 21 species worldwide. The remaining three cicada-killing species in the genus in North America are:

• Sphecius convallis, the Pacific cicada killer, occurs in the western U.S. and in Mexico.
• Sphecius grandis, the western cicada killer, occurs in the mid- and western U.S. and in Mexico.
• Sphecius hogardii, the Caribbean cicada killer, occurs in the U.S. in Florida and in the Caribbean.

It is suspected that the western cicada killer represents more than one species. There is also evidence to suggest that the eastern cicada killer either has a subspecies or a closely related species that mimics the Pacific cicada killer. Alternatively, when they were already distinct species, significant hybridization has occurred between them, though not enough to fully overcome their present reproductive isolation.^[3]

The spectacled cicada killer, Sphecius spectabilis (Taschenberg, 1875), is found in the South American countries of Argentina, Bolivia, Brazil, Chile, Colombia, French Guiana, Paraguay, Surinam and Venezuela.

Sixteen other cicada killer wasp species in the genus Sphecius are found in Europe, the Middle East, Africa and Asia. There are also other genera of cicada-killing wasps (e.g., Liogorytes in South America and Exeirus in Australia) which are the "cicada killers" of their native lands.

References